Position detection device and position indicator

ABSTRACT

An active stylus is provided, which can reduce battery power consumption and reduce the time required for its signal transmission. A position detection device includes a tablet and the stylus having a built-in power source, which are capable of bi-directional transmission and reception of signals through capacitive coupling therebetween. The tablet is configured to transmit a trigger signal US_trg and then transmit a command signal US_cmd to the stylus. The trigger signal US_trg causes the stylus to start its command information receiver to receive the command signal US_cmd including information for controlling the stylus.

BACKGROUND Technical Field

The present disclosure relates to a position detection device and aposition indicator and, more particularly, to a position detectiondevice that obtains a position pointed to by a position indicator on atablet through capacitive coupling between the tablet and the positionindicator, which is of a type having a built-in power source, and tosuch position indicator.

Description of the Related Art

There is known a position detection device including a tablet and anactive stylus (simply referred to as “stylus” hereinafter), which is aposition indicator of a built-in power source type, wherein the tabletand the stylus are coupled through capacitive coupling for signaltransmission. This type of position detection device is configured suchthat the stylus transmits signals and the tablet receives the signals ina one-way communication. An example of the position detection device ofthis type is disclosed in Patent Document 1.

Another example of the position detection device is disclosed in PatentDocument 2. This position detection device is constructed as follows. Astylus is provided with an electrode and a battery for signaltransmission, and the stylus detects a pen pressure and transmits thepen pressure detection result in digital signals. A tablet is composedof a display unit and a transparent sensor, and the transparent sensorpermits detection of the position pointed to by the stylus and the penpressure as well as the position touched by a finger.

PRIOR ART DOCUMENT Patent Documents

Patent Document 1: PCT Patent Publication No. 2014/051296

Patent Document 2: Japanese Patent Laid-open No. 2014-63249

Patent Document 3: Japanese Patent Laid-open No. 2015-103143

BRIEF SUMMARY Technical Problem

The position detection device disclosed in Patent Document 1 has adisadvantage as described below. The conventional stylus has an uniqueIDentification data (unique IDentification (ID)) stored therein, and isso constructed as to transmit the unique ID together with other signalsto the tablet. The unique ID is a piece of data that may be larger than60 bits, as disclosed in Patent Document 1, and thus the unique ID mayrequire a long time for transmission.

The conventional position detection device containing the stylus isdesigned for one-way transmission from the stylus to the tablet, whichrequires the stylus to continue transmitting signals even when it is noton the tablet. Due to such continuous transmission of signals, theconventional stylus suffers from excessive battery consumption.

Moreover, the unique ID described above is information which needs notbe transmitted repeatedly from the position indicator, once the tabletrecognizes the position indicator, while the stylus remains on thetablet. The conventional stylus disclosed in Patent Document 1 transmitsthe unique ID repeatedly, which causes the position indicator to take along time for signal transmission. This also leads to further batteryconsumption.

Thus, it is an aspect of the present disclosure to provide a positiondetection device and a position indicator, wherein the positiondetection device is characterized in that a stylus (which is a positionindicator with a built-in power source) reduces battery consumption andreduces the time required for signal transmission.

Technical Solution

A position detection device according to the present disclosure isconfigured to obtain a pointed position on a tablet by a positionindicator through capacitive coupling between the tablet and theposition indicator. The position detection device has the basicconstruction as explained in the following.

The tablet transmits to the position indicator a first control signaland a second control signal, which are different from each other interms of frequencies or modulation methods, to control the positionindicator. The position indicator has a power source and transmits atleast a position indicating signal to the tablet. The position indicatorincludes a first control signal receiver that receives the first controlsignal and a second control signal receiver that receives the secondcontrol signal, respectively. (Basic structure 1)

In the position detection device characterized by the basic structure 1,the first control signal may have a single frequency and not modulated,and the second control signal may be modulated with binary data. (Basicstructure 2)

In the position detection device characterized by the basic structure 2,the position indicator may operate in a first operation mode which onlyreceives the first control signal, and in a second operation mode whichtransmits at least the position indicating signal and receives thesecond control signal repeatedly. The position indicator in the firstoperation mode, once receiving the first control signal, transitionsfrom the first operation mode to the second operation mode. (Basicstructure 3)

In the position detection device characterized by the basic structure 3,the position indicator may include unique ID information or include apen pressure detection circuit, and transmit a data signal modulatedaccording to the unique ID information or pressure information detectedby the pen pressure detection circuit. The position indicator may beconfigured to select, based on the second control signal received, oneof the unique ID information, the pen pressure information, and otherinformation, according to which to modulate a data signal to betransmitted. (Basic structure 4)

A position indicator according to another aspect of the presentdisclosure obtains a pointed position on a tablet through capacitivecoupling between the position indicator and the tablet. The positionindicator generates a transmitting signal by resonance generated by aresonance circuit including a transformer primary coil and a capacitor.The position indicator also includes a control signal receiving circuitconnected to a transformer secondary coil, to which an electrode isconnected. The control signal is transmitted from the tablet with afrequency close to a resonant frequency of the resonance circuit.

Advantageous Effect

The position detection device according to the present disclosure ischaracterized as follows. The tablet transmits to the position indicatorthe first control signal having a single frequency and the secondcontrol signal which has been modulated with binary data. The positionindicator, when not on the tablet, does not transmit the positionindicating signal nor receive the second control signal, which wouldrequire large power consumption; rather, it only receives the firstcontrol signal with minimum power consumption. Thus, the positionindicator can suppress excessive power consumption.

Further, the position indicator can adjust what information is to betransmitted as a digital signal, in response to the second controlsignal received. This eliminates the need for the position indicator toalways transmit the unique ID together with the information of penpressure. This permits the position indicator to reduce the timerequired for signal transmission, which leads to further power saving.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram depicting the structure of a position detectiondevice 1 according to a first embodiment of the present disclosure.

FIG. 2 is a diagram depicting the internal structure of a tablet 3depicted in FIG. 1.

FIG. 3 is a diagram depicting the internal structure of a stylus 2depicted in FIG. 1.

FIG. 4 is a flowchart depicting the processing in the tablet 3 accordingto the first embodiment of the present disclosure.

FIG. 5 is a flowchart depicting the processing in the stylus 2 accordingto the first embodiment of the present disclosure.

FIG. 6 is a diagram depicting the timing for signal transmission andreception between the stylus 2 and the tablet 3 according to the firstembodiment of the present disclosure.

FIG. 7 is a flowchart depicting the processing in the tablet 3 accordingto a second embodiment of the present disclosure.

FIG. 8 is a flowchart depicting the processing in the stylus 2 accordingto the second embodiment of the present disclosure.

FIG. 9 is a diagram depicting the timing for signal transmission andreception between the stylus 2 and the tablet 3 according to the secondembodiment of the present disclosure.

FIG. 10 is a diagram depicting the internal structure of the stylus 2according to a third embodiment of the present disclosure.

FIG. 11 is a diagram depicting the timing for signal transmission andreception between the stylus 2 and the tablet 3 according to the thirdembodiment of the present disclosure.

FIG. 12 is a diagram depicting the timing for signal transmission andreception between the stylus 2 and the tablet 3 according to amodification of the first embodiment of the present disclosure.

FIG. 13 is a diagram depicting an example of a command signal as thespectrum spread code.

FIG. 14 is a diagram depicting an example of the structure of a matchedfilter circuit.

FIG. 15 is a diagram depicting the relation between each step and itsoutput in FIG. 14.

FIG. 16 is a diagram depicting an example of the internal structure ofthe stylus 2.

FIG. 17 is a diagram depicting an example of the internal structure ofthe stylus 2 according to a modification of the third embodiment.

FIG. 18 is a diagram depicting an example of the internal structure ofthe stylus 2 according to a modification of the third embodiment.

DETAILED DESCRIPTION

The preferred embodiments of the present disclosure will be describedbelow in more detail with reference to the accompanying drawings.

According to a first embodiment of the present disclosure, a positiondetection device 1 is configured as depicted in FIG. 1. It is noted fromFIG. 1 that the position detection device 1 is composed of a stylus 2,which functions as a position indicator, and a tablet 3. The tablet 3has the internal structure as depicted in FIG. 2. The stylus 2 has theinternal structure as depicted in FIG. 3.

The stylus 2 is a device resembling a pen. As depicted in FIG. 1, it iscomposed of a core 20, an electrode 21, a pen pressure detecting sensor(a pen pressure detection circuit) 23, a circuit board 24, and a battery25 (a power source).

The core 20 is a rod-like member, and is arranged such that the pen axisdirection of the stylus 2 coincides with the lengthwise direction of thecore 20. The core 20 has its tip 20 a coated with a conductive material,which forms the electrode 21. The electrode 21 may be formed of aconductive material embedded in the core 20. The pen pressure detectingsensor 23 is physically connected to the core 20, to detect the penpressure applied to the tip 20 a of the core 20. The pen pressuredetecting sensor 23 may use a capacitor, which varies its capacitance inresponse to the pen pressure, as described in Patent Document 2.

The electrode 21 is electrically connected to the circuit board 24, anddetects control signals US (a trigger signal US_trg and a command signalUS_cmd, as depicted in FIG. 1) transmitted from the tablet 3 andtransmits stylus signals DS (a position signal DS_pos and a data signalDS_res, as depicted in FIG. 1) to the tablet 3. Alternatively, theelectrode to receive the control signals US may be provided separatelyfrom the electrode to transmit the stylus signals DS.

The tablet 3 is composed of a flat sensor 30 and a sensor controller 31.The tablet 3 also includes a sensor surface 3 a on the top of the sensor30.

The tablet 3 has the internal structure as depicted in FIG. 2. Thesensor 30 is composed of linear electrodes 30X and linear electrodes30Y, which are extending in the X and Y directions respectively at equalintervals and which intersect with each other at right angles, therebyforming a matrix pattern. Though not illustrated, the sensor 30 includesa substrate of a transparent glass plate, and the linear electrodes 30Xand 30Y are arranged on the back surface (an inside surface) of thetransparent glass plate. The front surface (an outside surface) of thesubstrate forms the sensor surface 3 a of the tablet 3. There may be aninstance in which the tablet 3 is provided with the sensor surface 3 afunctioning as a display. In this case, the substrate is arranged on adisplay surface of the display device (not depicted) such as a liquidcrystal display, and the linear electrodes 30X and 30Y are arrangedbetween the liquid crystal display and the substrate, wherein the linearelectrodes 30X and 30Y are preferably formed from a transparentconductor such as ITO (indium tin oxide).

The tablet 3 is constructed to detect not only the stylus 2 but also ahuman finger 4, as depicted in FIG. 2. Moreover, the tablet 3 isdesigned to perform two types of detection by time division because thedetection system applicable to the stylus 2 differs from the detectionsystem applicable to the finger 4, as will be more fully describedbelow.

The sensor controller 31 is composed of a selecting circuit 41, aselecting circuit 42, a control circuit 43, switches 44 and 45, anamplifying circuit 46, a gain control circuit 47, a band-pass filter 48,a demodulating circuit 49, an analog-digital converter (AD converter)50, and a memory controller (MCU) 51, as depicted in FIG. 2.

The selecting circuit 41 selects one or more adjoining ones of thelinear electrodes 30X in response to a control signal d from the controlcircuit 43. Also, the selecting circuit 42 selects one or more adjoiningones of the linear electrodes 30Y in response to a control signal c fromthe control circuit 43.

The selecting circuit 41 and the selecting circuit 42 respectivelyselect the X-electrode(s) and the Y-electrode(s), either of which issubsequently connected to the amplifying circuit 46 through the switch45.

The amplifying circuit 46 amplifies the signal from the stylus 2, andthe amplified signal has its gain controlled to a certain level by thegain control circuit 47. The gain-controlled signal enters the band-passfilter 48, which passes only that component which has the frequency ofthe signal transmitted from the stylus 2. The filtered signal isdemodulated by the demodulating circuit 49. The demodulated signalpasses through the analog-digital converter (AD converter) 50 and isconverted into the output signal representing the level of the signalreceived from the stylus 2.

The switch 44 controls whether the Y-electrode(s) selected by theselecting circuit 42 should be used for signal reception or for signaltransmission. The Y-electrode(s) selected by the selecting circuit 42 isconnected to the amplifying circuit 46 through the switch 45 when acontrol signal b from the control circuit 43 is at a low level “0.” TheY-electrode(s) selected by the selecting circuit 42 is supplied with atransmitting signal a from the control circuit 43 when the controlsignal b from the control circuit 43 is at a high level “1” and thetransmitting signal a is transmitted from the sensor 30.

The tablet 3 has five operation modes, and the control circuit 43 maysequentially switch through the five modes to control respectivecircuits in the sensor controller 31, as will be described below. Eachof the five operation modes will be described in detail.

The first mode is intended to detect the position of the finger 4. Inthis mode, the control circuit 43 assigns the control signal b to thehigh level “1” and assigns a control signal e to the low level “0.” TheY-electrode selected by the selecting circuit 42 is supplied with thetransmitting signal a from the control circuit 43, so that the sensor 30transmits the touch detecting signal. On the other hand, the X-electrodeselected by the selecting circuit 41 is connected to the amplifyingcircuit 46. At this time, the control circuit 43 carries out control inresponse to a control signal g such that the band-pass filter 48produces the center frequency coinciding with the frequency of the touchdetecting signal. According to this configuration, the MCU 51 senses achange in the touch detecting signal due to the finger 4 touching thesensor surface 3 a, thereby deriving the coordinate position of thefinger 4.

The second mode is intended to transmit the trigger signal US_trg (afirst control signal; see FIG. 1) to the stylus 2. In this mode, thecontrol circuit 43 assigns the control signal b to the high level “1” sothat the Y-electrode selected by the selecting circuit 42 is suppliedwith the transmitting signal a from the control circuit 43 and thesensor 30 transmits the trigger signal US_trg. The transmitting signal ain this case is identical with the trigger signal US_trg, which isgenerated by the trigger signal transmitter 43 a (a first control signaltransmitter) that forms part of the control circuit 43. The transmittingsignal a (the trigger signal US_trg) preferably has the same frequencyas the signal transmitted by the stylus 2, as will be described later.Moreover, the trigger signal US_trg should preferably be a signal whichis not modulated and has a single frequency.

In this case, the selecting circuit 42 may select an electrode from someof the electrodes 30Y that are close to the position pointed to by thestylus 2 to transmit the trigger signal US_trg from the selectedelectrode, or may select all of the electrodes 30Y at once to transmitthe trigger signal US_trg from all of the electrodes.

The third mode is intended to transmit the command signal US_cmd (asecond control signal; see FIG. 1) to the stylus 2. In this mode also,the control circuit 43 assigns the control signal b to the high level“1” so that the Y-electrode selected by the selecting circuit 42 issupplied with the transmitting signal a from the control circuit 43. Thetransmitting signal a in this case is identical with the command signalUS_cmd, which is generated by the command signal transmitter 43 b (asecond control signal transmitter) that forms part of the controlcircuit 43. The transmitting signal a is a signal modulated according tothe control information that controls the stylus 2 (command informationCmd, to be described later). The command signal US_cmd in thisembodiment is a spectrum spread code.

The spectrum spread code as an example of the transmitting signal a isdepicted in FIG. 13. In FIG. 13, transmission of 3-bit commandinformation (1,0,1) is assumed, with the spread code being “0x1AD3.” Inother words, the output signal changes in the order of “0x1AD3” when thedata being transmitted is “1,” and the output signal changes in theorder of “0xE54C,” which is an inverse of “0x1AD3,” when the data beingtransmitted is “0.” It is assumed in FIG. 13 that transmission isperformed sequentially from the upper bit of the spread code.

In this case also, the selecting circuit 42 may select an electrode fromsome of the electrodes 30Y that are close to the position pointed to bythe stylus 2 to transmit the command signal US_cmd from the selectedelectrode, or may select all of the electrodes 30Y at once to transmitthe command signal US_cmd from all of the electrodes.

The fourth mode is intended to detect the position signal DS_postransmitted from the stylus 2, thereby determining the position of thestylus 2. In this mode, the control circuit 43 assigns the controlsignal b to the low level “0” so that the Y-electrode selected by theselecting circuit 42 is connected to the amplifying circuit 46 throughthe switch 45. Also, the control circuit 43 transmits the control signalg to control the center frequency of the band-pass filter 48 to coincidewith the frequency of the signal transmitted from the stylus 2.

According to this embodiment, when a coordinate of the stylus 2 on the Xaxis is to be obtained, the control circuit 43 assigns the controlsignal e to the low level “0” and connects the X-electrode selected bythe selecting circuit 41 to the amplifying circuit 46. The MCU 51 readsthe data output from the AD converter 50 as the signal level value whilesequentially selecting a plurality, for example five, of X-electrodesselected by the selecting circuit 41, around the X-electrode closest tothe position pointed to by the stylus 2. The MCU 51 determines theX-coordinate of the stylus 2 from the signal level distribution amongthe selected X-electrodes.

When a coordinate of the stylus on the Y axis is to be determined, thecontrol circuit 43 assigns the control signal e to the high level “1”and connects the Y-electrode selected by the selecting circuit 42 to theamplifying circuit 46. The MCU 51 reads the data output from the ADconverter 50 as the signal level value while sequentially selecting aplurality, for example five, of Y-electrodes selected by the selectingcircuit 42, around the Y-electrode closest to the position pointed to bythe stylus 2. The MCU 51 determines the Y-coordinate of the stylus 2from the signal level distribution among the selected Y-electrodes.

The fifth mode is intended to receive the data signal DS_res (seeFIG. 1) from the stylus 2. For reception of the data signal DS_res,either the X-electrode or the Y-electrode may be used. The followingdescribes an instance in which the X-electrodes are used to receive thedata signal DS_res. In this mode, the control circuit 43 assigns thecontrol signal e to the low level “0” so that the X-electrode selectedby the selecting circuit 41 is connected to the amplifying circuit 46.The control circuit 43 performs control according to the control signalg so that the center frequency of the band-pass filter 48 coincides withthe frequency of the signal transmitted from the stylus 2. The controlcircuit 43 operates such that the selecting circuit 41 selects several,for example three, X-electrodes at once, which are around theX-electrode closest to the position pointed to by the stylus 2. The MCU51 periodically reads the output from the AD converter 50.

In a case where the data signal DS_res is received by way of theY-electrode, the control signal b should be assigned to the low level“0” and the control signal e should be assigned to the high level “1.”

The foregoing has described how the control circuit 43 operates in eachof the five modes. It should be understood from the foregoingdescription that the tablet 3 is so configured as to performtransmission and reception of signals by using the same sensor 30. Theconfiguration of the tablet 3 depicted in FIG. 2 will be described inmore detail below.

The amplifying circuit 46 amplifies the signal which is induced in anyone of the electrodes 30X and 30Y selected by the selecting circuits 41or 42. The gain control circuit 47 further amplifies the signal receivedfrom the amplifying circuit 46, such that it has its amount ofamplification controlled by the control signal f from the controlcircuit 43. The gain control circuit 47 sends its output to theband-pass filter 48.

The band-pass filter 48 is a filter circuit which only allows passage ofsignals having a certain bandwidth around a defined center frequency.The center frequency is controlled by the control signal g received fromthe control circuit 43. In the mode of detecting the position of thefinger 4 described above, the control circuit 43 controls the band-passfilter 48 such that the center frequency coincides with the frequency ofthe touch detecting signal. Moreover, in the mode of detecting theposition of the stylus 2, the control circuit 43 controls the band-passfilter 48 such that the center frequency coincides with the frequency ofthe position signal DS_pos (see FIG. 1). In addition, in the mode ofreceiving the data signal DS_res (see FIG. 1), the control circuit 43controls the band-pass filter 48 such that the center frequencycoincides with the frequency of the data signal DS_res. It is assumed inthis embodiment (depicted in FIG. 3) that the position signal DS_pos andthe data signal DS_res have the same frequency.

The signal for finger detection and the signal for stylus detection(position signal DS_pos and data signal DS_res) preferably differ fromeach other in terms of their frequency bands. This configuration permitsthe band-pass filter 48 to discriminate between these signals. The datasignal DS_res may be that of single frequency, or may contain more thanone frequency component. In the latter case, it is desirable that thecontrol circuit 43 controls the bandwidth of the band-pass filter 48 sothat all of these frequencies are included.

The demodulating circuit 49 is a circuit which generates a voltagecorresponding to the level of the output signal from the band-passfilter 48. The AD converter 50 performs analog-digital conversion atdefined time intervals on the voltage corresponding to the levelreceived from the demodulating circuit 49, thereby generating digitalsignals. The AD converter 50 controls the sampling time intervals inresponse to a control signal h from the control circuit 43. The ADconverter 50 outputs the digital data to be read by the MCU 51.

The MCU 51 is a microprocessor including read-only memory (ROM) andrandom-access memory (RAM) and configured to operate according to adefined program. The MCU 51 controls the control circuit 43 to cause itto output the signals a to h. The MCU 51 also reads and processes thedigital data from the AD converter 50.

The control circuit 43 is a logic circuit that outputs the signals a toh at timings specified by the instruction from the MCU 51.

The foregoing is a description of the configuration and operation of thetablet 3. The following is a detailed description of the configurationand operation of the stylus 2. FIG. 16 is a diagram depicting an exampleof the internal structure of the stylus 2. FIG. 3 is a diagram depictingthe internal structure of a stylus 2.

The circuit board 24 depicted in FIG. 3 includes three switches SW1 toSW3, a controller 60, an oscillating circuit 61, a transformer 62, atrigger signal detector 63, and a command information receiver 64.

The oscillating circuit 61 performs oscillation in accordance with anoscillation control signal Ocn supplied from the controller 60. Theoscillating circuit 61 also includes an inductance-capacitance (LC)resonance circuit 61 a composed of a coil and a capacitor.

The transformer 62 is composed of a primary coil (a first coil) and asecondary coil (a second coil), which are coupled with each other. Theprimary coil functions as a coil for the LC resonance circuit 61 a. Thesecondary coil is connected to the electrode 21 through the switch SW1.

The trigger signal detector 63 is designed to receive the trigger signalUS_trg from the tablet 3; that is, the trigger signal detector 63 is afirst control signal receiver. The trigger signal detector 63 iscomposed of an amplifying circuit 63 a and a demodulating circuit 63 b.The amplifying circuit 63 a is designed to amplify the trigger signalUS_trg, which is induced in the electrode 21. The demodulating circuit63 b examines the output signal from the amplifying circuit 63 a to seeif it has a higher level than a defined level and then outputs it as adetected signal Det. The electrode 21 and the amplifying circuit 63 aare connected to each other through the switches SW1 and SW2.

The level of the detected signal Det is high when the electrode 21 hasreceived the trigger signal US_trg, and is low when the electrode 21 hasnot received the trigger signal US_trg. Thus, the trigger signaldetector 63 can output the detected signal Det in a binary form based onthe presence and absence of the trigger signal US_trg, without having toperform a specific decoding operation.

The trigger signal detector 63 receives the trigger signal US_trg whilethe input of the amplifying circuit 63 a is connected to the transformer62. Since the primary side of the transformer 62 forms the LC resonancecircuit 61 a, by making the trigger signal US_trg coincide with theresonance frequency of the LC resonance circuit 61 a, one can achievethe trigger signal detector 63 that detects only the trigger signalUS_trg from among signals induced in the electrode 21.

The command information receiver 64 receives the command signal US_cmdfrom the tablet 3; that is, the command information receiver 64functions as a second control signal receiver. The command informationreceiver 64 is composed of an AD converter 64 a and a matched filtercircuit 64 b. FIG. 14 is a diagram depicting an example of a structureof the matched filter circuit 64 b. As illustrated in FIG. 14, thematched filter circuit is composed of a shift register (R0 to R31) thatstores 12-bit data in 32 steps, a 16-bit register (K0 to K15) thatstores a predetermined KEY code, and an arithmetic unit that performsarithmetic operation on the values stored in the shift registers and theKEY code. The arithmetic unit includes a 16-bit register (Q0 to Q15)that stores the results of operation.

The command information receiver 64 is connected to the electrode 21through the switch SW3, so that it receives the command signal US_cmdwhen the switch SW3 is turned on and the switch SW1 is turned off. Theoperation of the command information receiver 64 will be described inmore detail later. This type of circuit consumes a lot of electric powerbecause it needs operation at a high clock rate. To address this issue,the embodiment described herein is designed such that the commandinformation receiver 64 suspends its operation in response to thecontrol signal En generated by the controller 60. Specifically, thecommand information receiver 64 is configured to operate when thecontrol signal En is active (at a high level) and to become idle whenthe control signal En is inactive (at a low level). While being idle,the command information receiver 64 consumes very little power and doesnot receive the signal supplied to its input end. Because the controller60 is so configured as to activate the control signal En in response tothe trigger signal US_trg received prior to the command signal US_cmd,however, the stylus 2 can reliably receive the command signal US_cmd.This will be described in more detail later.

The controller 60 turns on and off the switches SW1 to SW3 in responseto the control signal SWC, activates and inactivates the commandinformation receiver 64 with the control signal En, generates theoscillation control signal Ocn, and allows the pen pressure detectingsensor 23 to detect a pen pressure. The controller 60 is formed of amicroprocessor (MPU) that operates in accordance with a defined program.Each of the components will be described in more detail below.

In the present embodiment, the pen pressure detecting sensor 23 uses acapacitor which varies its capacitance in accordance with pen pressure.Pen pressure detection may be performed using the method disclosed inPatent Document 3, and its detailed description is omitted.

The controller 60 turns on and off the switches SW1 to SW3 and generatesthe control signal En as depicted in Table 1.

TABLE 1 Corresponding mode for Action of Timing tablet 3 SW1 SW2 SW3 Enstylus 2 Initial state Mode to detect on on off Inactive Reception ofposition of trigger signal finger 4 US_trg Mode to transmit triggersignal US_trg After Mode to on on/off on Active Reception of receptionof transmit command trigger command signal signal signal US_cmd US_cmdUS_trg After Mode to detect on off off Inactive Transmission receptionof position of of position command stylus 2 signal signal DS_pos US_cmdAfter Mode to receive on off off Inactive Transmission transmission datasignal of data signal of position DS_res DS_res signal DS_pos

As shown in Table 1, the controller 60 in its initial state (when thestylus 2 is not placed on the tablet 3) keeps the switches SW1 and SW2on and switch SW3 off so that the command information receiver 64 is inan operation-suspended state. Under this condition, the electrode 21 isconnected to the trigger signal detector 63, and the trigger signalUS_trg is received, as depicted in Table 1. The fact that the commandinformation receiver 64 remains idle helps the stylus 2 to reduce powerconsumption.

After the trigger signal US_trg has been received, that is, after thedetected signal Det has turned into a high level, the controller 60turns the switch SW1 off and turns the switch SW3 on. Also, the controlsignal En is made active, so that the command information receiver 64becomes operable. The switch SW2 may remain on or may be turned off. Inthis way, the electrode 21 is connected to the command informationreceiver 64 and the command information receiver 64 becomes active, sothat the command signal US_cmd is received as depicted in Table 1. Thus,the command information receiver 64 receives the command signal US_cmdand then outputs the command information Cmd, which is temporarilystored in the controller 60.

Here, the controller 60 may select either the first operation mode orthe second operation mode, with the former being intended for low-speedoperation mode with low power consumption and the latter being intendedfor high-speed operation mode with high power consumption. Thecontroller 60 in its low-speed operation mode can receive the detectedsignal Det (which is a simple binary signal), but cannot receive andprocess complex signals such as command information Cmd and cannottransmit the position signal DS_res and the data signal DS_pos. Forthese operations to be performed, the controller 60 should be turnedinto the high-speed operation mode. Therefore, the controller 60illustrated in this embodiment should preferably be configured such thatit autonomously transitions from the low-speed operation mode to thehigh-speed operation mode in response to the detected signal Detchanging from the low level to the high level, that is, in response tothe trigger signal US_trg being received. Preferably, the controller 60may be configured such that it returns to the low-speed operation modeafter the data signal DS_res has been transmitted. This way thecontroller 60 may minimize power consumption. The description continueson the assumption that the controller 60 is compatible with the twomodes described above.

The controller 60 stores therein the command information Cmd receivedfrom the command information receiver 64 having received the commandsignal US_cmd, and then the controller 60 turns the switch SW1 on, theswitch SW2 off, and the switch SW3 off. In addition, the controller 60inactivates the control signal En so that the command informationreceiver 64 returns to its suspended state. Further, the controller 60keeps the oscillation control signal Ocn at a high level for a certainperiod of time, so that the oscillating circuit 61 (a positionindicating signal transmitter) becomes active. As a result, theelectrode 21 generates the position signal DS_pos (a position indicatingsignal) and transmits it continuously for a certain period of time.During this transmission, the tablet 3 receives the position signalDS_pos, thereby determining the position pointed to by the stylus 2.

After having transmitted the position signal DS_pos, while thecontroller 60 keeps the switches SW1 to SW3 and the control signal En inthe same state as before, the controller 60 generates the oscillationcontrol signal Ocn and transmits it to the oscillating circuit 61,thereby causing the oscillating circuit 61 to generate the data signalDS_res in response to the command information Cmd stored in thecontroller 60. The apparatus configured as depicted in FIG. 3 generatesthe data signal DS_res, which is an OOK (On-Off Keying)-modulatedsignal. As a result of the foregoing operation, the controller 60 causesthe electrode 21 to transmit the OOK-modulated data signal DS_res, whichis received by the tablet 3 as described above. Thereafter, thecontroller 60 returns to the initial state.

The following description in reference to FIGS. 13 and 14 relates to howthe command information receiver 64 extracts the command information Cmdfrom the command signal US_cmd. The matched filter circuit 64 b (FIG.14) receives the output (D0 to D11) and clock signal (CLK) from the ADconverter 64 a. The clock signal has the same frequency as the samplingfrequency of the AD converter 64 a, and preferably has a frequency whichis an integer multiple of one step cycle of the spread code as depictedin FIG. 13. In the illustrate embodiment, the sampling frequency of theAD converter 64 a is twice the step cycle of the spread code depicted inFIG. 13. Also, the controller 60 supplies the reset signal (Reset) (notdepicted), which clears the values of the shift register (R0 to R31) andthe values of the register (Q0 to Q15) of the arithmetic unit. Thedescription of this embodiment is based on the assumption that the data(D0 to D11) from the AD converter 64 a is captured at the leading edgeof the clock signal (CLK) for the arithmetic unit to perform arithmeticoperation.

The KEY code (k0 to k15) holds “0x1AD3” which is identical with thespread code of the command signal US_cmd (FIG. 13) transmitted from thetablet. That is, since this embodiment assumes that transmission startsfrom the higher-order bit, the KEY code takes the values of k0=1, k1=1,k2=0, k3=0, k4=1 . . . k15=0. The arithmetic unit calculates the totalsum by addition or subtraction of each data stored in the shift register(R0 to R31), and outputs the result in terms of Q0 to Q15. This output(Q0 to Q15) represents the coded data. Here, since k0=1, each value ofthe shift register R0 and R1 is added to Q0 to Q15. Also, since k1=1,each value of the shift register R2 and R3 is added to Q0 to Q15. Sincek2=0, each value of the shift register R4 and R5 is subtracted from Q0to Q15. The thirty-two results of AD conversion (R0 to R31) undergoaddition or subtraction, and are outputted as Q0 to Q15. The reason whyprocessing is performed on two consecutive values of the shift register(R0 to R31) in response to each value of k0 to k15 is that the presentembodiment is designed such that the sampling frequency of the ADconverter 64 a is twice the step cycle of the spread code depicted inFIG. 13.

FIG. 15 depicts the relation between each step (each rising edges ofCLK) as depicted in FIG. 14 and its output. The controller 60, afterreceiving the trigger signal US_trg, activates the control signal En asdepicted in Table 1, and sends the reset signal (Reset) to the matchedfilter circuit 64 b. This results in the shift register (R0 to R31)being cleared, so that the output (Q0 to Q15) from the arithmetic unitbecomes null. The present embodiment requires that the commandinformation receiver 64 of the stylus 2 becomes active before the tablettransmits the command signal US_cmd. This is illustrated in FIG. 15 onthe assumption that the first clock (CLK) that follows the reset signal(Reset) rises immediately after the tablet has started transmitting thecommand signal US_cmd (FIG. 13).

FIG. 15 depicts that the output (Q0 to Q15) from the matched filtercircuit 64 b shifts toward a large positive value at the 32-nd step andshifts toward a large negative value at the 64-th step, and shifts againtoward a large positive value at the 96-th step. Thus, the controller 60detects the command information Cmd transmitted from the tablet as(1,0,1).

The foregoing is a description of the structure and operation of thestylus 2. The following is a general description of how the positiondetection device operates according to the present embodiment withreference to FIGS. 4 and 5 that depict process flows and FIG. 6 thatdepicts timing of signal transmission and reception. FIG. 4 is a flowdiagram depicting how the tablet 3 performs processing according to thepresent embodiment. FIG. 5 is a flow diagram depicting how the stylus 2performs processing according to the present embodiment. FIG. 6 is adiagram depicting the timing of signal transmission and receptionbetween the stylus 2 and the tablet 3 according to the presentembodiment.

As depicted in FIGS. 4 and 6, the tablet 3 transmits the trigger signalUS_trg and the command signal US_cmd repeatedly and periodically (asnoted from Steps S301 and S303 in FIG. 4). The foregoing signaltransmission may be performed in a time-division manner so as toadditionally detect the finger 4, though description of finger detectionis omitted here. The following description is based on the assumptionthat the stylus 2 is placed on (DOWN) the sensor surface 3 a of thetablet 3 (FIG. 1) at time t1 (which denotes the time between the time atwhich the N-th trigger signal US_trg N is transmitted and the time atwhich the (N+1)-th trigger signal US_trg N+1 is transmitted) depicted inFIG. 6.

The stylus 2 in its initial state repeats reception of the triggersignal US_trg (as noted from Steps S401 and S403 in FIG. 5). As soon asthe stylus 2 approaches or contacts the sensor surface 3 a of the tablet3 at time t1, the stylus 2 receives the trigger signal US_trg N+1transmitted from the tablet 3 thereafter. As soon as the stylus 2receives the trigger signal US_trg N+1, the controller 60 switches fromthe STOP state (the low-speed operation mode described above) into theRUN state (the high-speed operation mode described above) (see Step S405in FIG. 5 and time t2 in FIG. 6). This change occurs as the detectedsignal Det (depicted in FIG. 3) reaches the high level.

The controller 60, which has turned into the RUN state, activates thecontrol signal En, thereby starting the command information receiver 64(tuning into the Enable state) (see Step S407 in FIG. 5 and time t2 inFIG. 6). The command information receiver 64, which has been started inthis manner, receives the trigger signal US_trg N+1 and the commandsignal US_cmd in succession from the tablet 3 (Step S409). Thereafter,the controller 60 inactivates the control signal En, thereby terminating(or turning into the Disable state) the command information receiver 64(see Step S411 in FIG. 5 and the time t3 in FIG. 6).

Next, the controller 60 performs a process in response to the content ofcommand information Cmd extracted from the command information receiver64 that has received the command signal US_cmd (see Step S413 in FIG.5). A typical example of the process will be explained below. Supposethat the command information Cmd is intended to acquire a value of penpressure. Then, the controller 60 sets the latest value P of penpressure (pen pressure information), which has been acquired from thepen pressure detecting sensor 23 depicted in FIG. 1, in the data signalDS_res. Also, when the command information Cmd is intended to cause thestylus 2 to acquire the unique stylus number SID (ID information), thecontroller 60 sets the stylus number SID, which has been stored in thememory unit (not depicted), in the data signal DS_res.

The controller 60 may perform, in response to the content of the commandinformation Cmd, various processes in addition to those described above.For example, it may detect the slide lever position of a slide leverprovided on the side of the stylus 2 and use the slide level positioninformation as the command information Cmd. Alternatively, thecontroller 60 may, in response to the content of the command informationCmd, alter the transmission timing of the position signal DS_pos, orchange the frequency of the position signal DS_pos or the data signalDS_res.

Next, the controller 60 transmits the position signal DS_pos and thedata signal DS_res sequentially (see Steps S415 and S417 in FIG. 5; seethe position signal DS_pos1 and the data signal DS_res1 in FIG. 6). Thecontroller 60, which has completed the transmission of the data signalDS_res, switches from the RUN state (the high-speed operation modedescribed above) into the STOP state (the low-speed operation modedescribed above) (see Step S419 in FIG. 5; see time t4 in FIG. 6). Onthe other hand, the tablet 3 transmits the command signal US_cmd andthen receives the position signal DS_pos (see Step S305 in FIG. 4). Ifthe tablet 3 successfully receives the position signal DS_pos (see StepS307 for affirmative judgment in FIG. 4), the tablet 3 subsequentlyreceives the data signal DS_res (see Step S309 in FIG. 4). If the tablet3 fails to receive the position signal DS_pos (see Step S307 fornegative judgment in FIG. 4), it returns to the step of transmitting thetrigger signal US_trg (see Step S301 in FIG. 4).

The foregoing operation completes the series of processes correspondingto the (N+1)-th trigger signal US_trg N+1. Thereafter, as depicted inFIG. 6, the tablet 3 transmits the (N+2)-th trigger signal US_trg N+2and then repeats the same processes as described above. The tablet 3 maytransmit the trigger signal US_trg either at a constant rate or at avariable rate. Moreover, the tablet 3 may be so adjusted as to transmitthe trigger signal US_trg at a variable rate in accordance with whetheror not it has received the position signal DS_pos or the data signalDS_res.

The tablet 3 receives the position signal DS_pos in the following way.When the stylus 2 is placed on the tablet 3 for the first time(DS_pos1), the tablet 3 performs signal reception while sequentiallyswitching the X-electrodes and the Y-electrodes which are selected bythe selecting circuit 41 and the selecting circuit 42 depicted in FIG.2. The tablet 3 calculates the X-coordinate and Y-coordinate for theposition pointed to by the stylus 2 from the electrode number of theelectrode, which has given the highest signal level, and thedistribution of signal levels around that electrode number.

Also, when the position pointed to by the stylus 2 is roughly known(after DS_pos2), the tablet 3, when receiving the position signalDS_pos, may need to receive signals from only several X-electrodes andY-electrodes around the known position. Thus, the tablet 3 can calculatethe X-coordinate and Y-coordinate of the position pointed to by thestylus 2 from the distribution of the signal levels.

As described above, the present embodiment offers an advantage that thestylus 2 does not receive the trigger signal US_trg when the stylus 2 isnot on the tablet 3 and hence the stylus 2 does not need to transmitsignals. This helps reduce battery power consumption in the stylus 2 ascompared to the conventional active stylus.

Moreover, the stylus 2 can be configured to only transmit theinformation requested by the command signal US_cmd, which helps reducethe time required by the stylus 2 for its signal transmission.

According to the present embodiment, the stylus 2 includes the commandinformation receiver 64, which receives the command signal US_cmd, andis capable of altering the content of the data signal DS_res in responseto the content of the received command information Cmd. Thisconfiguration obviates the necessity for the stylus to keep transmittingthe unique ID number, which does not need to be received more than once.As a result, the stylus can reduce the time required for tis signaltransmission and hence reduce power consumption.

Moreover, according to the present embodiment, the stylus 2 includes thetrigger signal detector 63, which detects the trigger signal US_trgseparately from the command signal US_cmd, so that the commandinformation receiver 64 is activated only when the trigger signaldetector 63 detects the trigger signal US_trg. This configurationpermits shortening the active time of the command information receiver64, which entails large power consumption, and hence contributes tofurther power saving in the stylus.

In addition, according to the present embodiment, the stylus 2 keeps thecontroller 60 in the low-speed operation mode until the data signalDS_res is transmitted and then the trigger signal US_trg is received.This helps the controller 60 to reduce power consumption. Thus, theembodiment described above permits the stylus 2 to reduce powerconsumption even further, as compared with the conventional activestylus.

Furthermore, the stylus 2 according to the present embodiment isconfigured such that the transformer 62, in which the secondary coil isthe coil of the LC resonance circuit 61 a for signal transmission, playsa role of a band-pass filter. This permits the stylus 2 to operate witha less number of parts than the conventional stylus which needs aseparate band-pass filter to receive the trigger signal US_trg.

The present embodiment employs the spectrum spread code as the commandsignal US_cmd to be transmitted by the tablet. This is not intended tolimit the scope of the present disclosure. It will be possible, forexample, to employ another modulating system which alters the frequencyor phase of the signal to be transmitted by the command information Cmd.In such a case, the stylus 2 will need the command information receiver64 to be modified in structure according to the modulating system. Nomatter what the modulating system may be, the signal detection involvingdecoding usually consumes a large amount of electric power, and thepresent embodiment offers the same technical advantage in this regard.

The second embodiment of the present disclosure will be described below.The tablet 3 and stylus 2 according to this embodiment are identical instructure with those depicted in FIGS. 1 to 3. The second embodimentdiffers from the first embodiment in the order of transmitting theposition signal DS_pos and the command signal US_cmd. They are identicalin other respects. The following description is focused mainly on thedifference between the two embodiments.

FIG. 7 is a flow diagram depicting a process by the tablet 3 accordingto the present embodiment. FIG. 8 is a flow diagram depicting a processby the stylus 2 according to the present embodiment. FIG. 9 is a diagramdepicting timing for the signals to be transmitted and received betweenthe stylus 2 and the tablet 3.

The tablet 3 according to the present embodiment has the control circuit43 as depicted in FIG. 2. As depicted in FIG. 7, the control circuit 43receives the position signal DS_pos from the stylus 2 (see Steps S305and S307 in FIG. 7), thereby detecting the position of the stylus 2, andthen transmits the command signal US_cmd (see Step S303 in FIG. 7). Thecommand signal US_cmd is transmitted only when the position signalDS_pos is received.

According to the present embodiment, the controller 60 in the stylus 2controls the switches SW1 to SW3 and the control signal En as depictedin Table 2.

TABLE 2 Corresponding Timing mode for tablet 3 SW1 SW2 SW3 En Action ofstylus 2 Initial state Mode to detect on on off Inactive Reception ofposition of trigger signal finger 4 US_trg Mode to transmit triggersignal US_trg After Mode to detect on off off Inactive Transmission ofreception of position of position signal trigger signal stylus 2 DS_posUS_trg After Mode to transmit on on/off on Active Reception oftransmission command signal command signal of position US_cmd US_cmdsignal DS_pos After Mode to receive on off off Inactive Transmission ofreception of data signal data signal command DS_res DS_res signal US_cmd

It is understood from comparison between Table 2 and Table 1 that thepresent embodiment differs from the first embodiment in that thetransmission of the position signal DS_pos precedes the reception of thecommand signal US_cmd. This is apparent from the flow diagram depictedin FIG. 8. The stylus 2 according to the present embodiment is soconstructed as to transmit the position signal DS_pos (see Step S415 inFIG. 8) and then starts the command information receiver 64 (see StepS407 in FIG. 8).

To realize the foregoing operation, the controller 60 according to thepresent embodiment receives the trigger signal US_trg (which brings thedetected signal Det to the high level) and then turns off the switchSW2. The switch SW1 and the switch SW3 remain on and off, and thecommand information receiver 64 also remains inactive. Thus, thecontroller 60 transmits the position signal DS_pos in the same way as inthe first embodiment.

As soon as the transmission of the position signal DS_pos is complete,the controller 60 starts control to receive the command signal US_cmd.That is, the controller 60 turns the switch SW1 off and turns the switchSW3 on and activates the control signal En, thereby activating thecommand information receiver 64. The switch SW2 may be left off orturned on. In this way, the command information receiver 64 receives thecommand signal US_cmd transmitted from the tablet 3, and the controller60 stores the command information Cmd.

The following process takes place during transition from S307 to S303,although not depicted in FIG. 7. The tablet 3 detects the end of theposition signal DS_pos and, after a certain length of time, starts thetransmission of the command signal US_cmd. During said time (the certainlength of time), the stylus 2 makes the command information receiver 64active.

The controller 60, which has stored the command information Cmd, turnsthe switch SW1 on and turns the switches SW2 and SW3 off and suspendsthe command information receiver 64. Then, the controller 60 transmitsthe data signal DS_res in response to the command information Cmd in thesame way as in the first embodiment.

According to the present embodiment, the tablet 3 transmits the triggersignal US_trg periodically and repeatedly as depicted in FIG. 9. And, attime t1, the stylus 2 placed on (DOWN) the sensor surface 3 a of thetablet 3 receives the trigger signal US_trg N+1, which has beentransmitted from the tablet 3, and turns the controller 60 into the RUNstate (the high-speed operation mode described above) at time t2 in FIG.9, and subsequently the controller transmits the position signal DS_pos(position signal DS_pos1 in FIG. 9). As soon as the transmission of theposition signal DS_pos is complete, the controller starts the commandinformation receiver 64 (turns into Enable state) (at time t3 in FIG. 9)to receive the command signal US_cmd1 transmitted from the tablet 3. Attime t4 after signal reception, the stylus terminates the commandinformation receiver 64 (turns into Disable state) and then transmitsthe data signal DS_res1 in the same way as depicted in FIG. 6. Thecontroller 60, which has transmitted the data signal DS_res, is switchedfrom the RUN state (the high-speed operation mode described above) intothe STOP state (the low-speed operation mode described above) at time t5depicted in FIG. 9.

According to the present embodiment, the foregoing operation completesthe series of processes corresponding to the (N+1)-th trigger signalUS_trg N+1. Thereafter, as depicted in FIG. 9, the tablet 3 transmitsthe (N+2)-th trigger signal US_trg N+2 and then repeats the sameprocesses as described above. In the present embodiment also, the tablet3 may transmit the trigger signal US_trg either at a constant rate or ata variable rate. Moreover, the tablet 3 may be so adjusted as totransmit the trigger signal US_trg at a variable rate in accordance withwhether or not it has received the position signal DS_pos or the datasignal DS_res.

As described above, the present embodiment, too, offers an advantagethat the stylus 2 does not receive the trigger signal US_trg when thestylus 2 is not on the tablet 3 and hence the stylus 2 does not need totransmit signals. This helps reduce battery power consumption in thestylus 2 as compared to the conventional active stylus.

Moreover, the stylus 2 can be configured to only transmit theinformation requested by the command signal US_cmd, which helps reducethe time required by the stylus 2 for its signal transmission.

According to the present embodiment also, the stylus 2 includes thecommand information receiver 64, which receives the command signalUS_cmd, and is capable of altering the content of the data signal DS_resin response to the content of the thus received command information Cmd.This configuration obviates the necessity for the stylus to keeptransmitting the unique ID number, which does not need to be receivedmore than once. As a result, the stylus can reduce time for its signaltransmission and hence reduces power consumption.

Moreover, according to the present embodiment also, the stylus 2includes the trigger signal detector 63, which detects the triggersignal US_trg separately from the command signal US_cmd, wherein whenthe trigger signal detector 63 detects the trigger signal US_rg, andafter the position signal DS_pos is transmitted, the command informationreceiver 64 is started. This configuration permits shortening the activetime of the command information receiver 64, which entails large powerconsumption, and hence contributes to further power saving in thestylus.

In addition, according to the present embodiment, the stylus 2 keeps thecontroller 60 in the low-speed operation mode until the data signalDS_res is transmitted and then the trigger signal US_trg is received.This helps the controller 60 to save power consumption. Thus, theembodiment described above permits the stylus 2 to reduce powerconsumption even further, as compared to the conventional active stylus.

Also, according to the present embodiment, the tablet 3 does not need totransmit the command signal US_cmd when the stylus 2 is not on thetablet 3. This leads to efficient use of time for detection of thefinger 4, for example.

The present embodiment also employs the spectrum spread code as thecommand signal US_cmd to be transmitted by the tablet. This is notintended to limit the scope of the present embodiment. It will bepossible to employ another modulating system as effectively as in thefirst embodiment.

The third embodiment of the present disclosure will be described below.The stylus 2 according to this embodiment differs from that in the firstembodiment in that the data signal DS_res is composed of BPSK-modulatedsignals. This difference makes the stylus 2 to differ in structure but,except for this difference, the stylus 2 according to the thirdembodiment is identical to the stylus 2 according to the secondembodiment. The following description is focused mainly on thedifference between the second embodiment and the third embodiment.

FIG. 10 is a diagram depicting the internal structure of the stylus 2according to the third embodiment. FIG. 11 is a timing chart for thesignals transmitted and received between the stylus 2 and the tablet 3according to the third embodiment.

In FIG. 10, corresponding components are given identical symbols asthose used in FIG. 3. The third embodiment (depicted in FIG. 10) isidentical with the first embodiment (depicted in FIG. 3) in thestructure of the electrode 21, the command information receiver 64, theAD converter 64 a, the matched filter circuit 64 b, the amplifyingcircuit 63 a, the demodulating circuit 63 b, and the pen pressuredetecting sensor 23.

The switch SW4 is intended to select one terminal from three terminalsa, b, and c and connects the selected terminal to the electrode 21. Theterminal a is connected to the trigger signal detector 71; the terminalb is connected to the command information receiver 64, and the terminalc is connected to the boosting circuit 74 (to be described later). Theswitch SW4 has its state controlled by the control signal SWC suppliedfrom the controller 70.

The transmitting signal generating circuit 73 generates signals inresponse to the demodulating signal Mod from the controller 70, whereinthe signals serve as the bases of the position signal DS_pos and datasignal DS_res. The boosting circuit 74 boosts the signal generated bythe transmitting signal generating circuit 73 up to a certain amplitude,thereby producing the position signal DS_pos and data signal DS_res.

The position signal DS_pos employed in the third embodiment is identicalwith that employed in the second embodiment. On the other hand, the datasignal DS_res employed in the third embodiment differs from that in thesecond embodiment in the method of demodulation. In the thirdembodiment, the data signal DS_res may be demodulated in various ways.For example, BPSK (Binary Phase Shift Keying) is a preferred method ofdemodulation. The following description assumes that the data signalDS_res is demodulated by the BPSK method. Thus, the transmitting signalgenerating circuit 73 demodulates the modulating signal Mod by the BPSKmethod, thereby generating the data signal DS_res.

The trigger signal detector 71 is composed of the trigger signaldetector 63 and the band-pass filter 71 a (filter circuit) that passescertain frequencies around the defined single frequency, wherein theband-pass filter 71 a is added to the preceding stage of the triggersignal detector 63 (preceding to the amplifying circuit 63 a). In otherwords, the stylus 2 according to the third embodiment does not containthe LC resonance circuit 61 a (in FIG. 3) and, consequently, it cannotlimit the band by the transformer 62, unlike the first embodiment. Toaddress this drawback in the third embodiment, the signals induced tothe electrode 21 are cleared of signal components having frequenciesoutside the frequency band of the trigger signal US_trg by using theband-pass filter 71 a. The amplifying circuit 63 a and the demodulatingcircuit 63 b perform processing in the same way as in the firstembodiment.

The controller 70 according to the third embodiment controls the switchSW4 and command information receiver 64 as depicted in Table 3.

TABLE 3 Corresponding State Timing mode for tablet 3 of SW4 En Action ofstylus 2 Initial state Mode to detect Selects Inactive Reception ofposition of terminal a trigger signal finger 4 Mode to transmit US_trgtrigger signal US_trg After Mode to detect Selects Inactive Transmissionof reception of position of terminal c position signal trigger signalstylus 2 DS_pos US_trg After Mode to transmit Selects Active Receptionof transmission command signal terminal b command signal of positionUS_cmd US_cmd signal DS_pos After Mode to receive Selects InactiveTransmission of reception of data signal terminal c data signal commandDS_res DS_res signal US_cmd

It is understood from Table 3 that the controller 70 in its initialstate causes the switch SW4 to select the terminal a and the commandinformation receiver 64 to be suspended. The mode of the controller 70in its initial state is the low-speed operation mode as described abovein the same way as in the first embodiment. In this way, the electrode21 is connected to the trigger signal detector 71, and the triggersignal US_trg is received as depicted in Table 3. In addition, thecommand information receiver 64 remains idle, so that the stylus 2reduces power consumption.

After the trigger signal US_trg has been received (or after the detectedsignal Det from the trigger signal detector 71 has taken on the highlevel), the controller 70 causes the switch SW4 to select the terminal cand turns itself into the high-speed operation mode described above.Furthermore, the controller 70 generates the modulating signal Mod,which permits the transmitting signal generating circuit 73 and theboosting circuit 74 to generate the position signal DS_pos, which is asignal of a single frequency. The generated position signal DS_pos isthen supplied to the transmitting signal generating circuit 73. As aresult, the electrode 21 sends out the position signal DS_pos to bereceived by the tablet 3 in the same way as in the second embodiment.

After having transmitted the position signal DS_pos, the controller 70causes the switch SW4 to select the terminal b and activates the controlsignal En, thereby activating the command information receiver 64. As aresult, the command information receiver 64 receives the command signalUS_cmd, and the controller 70 extracts the command information Cmd fromthe command signal US_cmd received by the command information receiver64 and stores the extracted command information Cmd.

After having received the command signal US_cmd, the controller 70causes the switch SW4 to select the terminal c and inactivates thecontrol signal En, thereby causing the command information receiver 64to be suspended. Then the controller 70 generates the modulating signalMod and supplies it to the transmitting signal generating circuit 73.The modulating signal Mod causes the transmitting signal generatingcircuit 73 to generate the data signal DS_res in response to the commandinformation Cmd which has been stored. As a result, the electrode 21transmits the BPSK-demodulated data signal DS_res, which is received bythe tablet 3 as in the case of the second embodiment.

The tablet 3 in the third embodiment may be constructed such that thedemodulating circuit 49 and the AD converter 50, which are depicted inFIG. 2, are replaced by the BPSK-demodulating circuit.

In a preferred form, the third embodiment causes the stylus 2 totransmit the data signal DS_res in synchronization with the reception ofsignal by the command information receiver 64. The matched filtercircuit 64 b produces its output, which varies with time as depicted inFIG. 15. The output values Q0 to Q15 fluctuate between a certainpositive level and a negative level, and some of them exceed thoselevels at the 32nd, 64th, and 96th steps (depicted in FIG. 15). Thesesteps coincide with the timing at which each bit of the command signalUS_cmd has been transmitted from the tablet 3 as depicted in FIG. 13.This means that if the stylus 2 transmits the data signal DS_res insynchronization with the command signal US_cmd, then the tablet 3 canreliably demodulate the BPSK signal.

According to the third embodiment, the data signal DS_res may be aBPSK-modulated signal. Except for this point, the third embodiment isidentical with the second embodiment and hence it also produces theeffect of reducing battery power consumption in the stylus 2.

The third embodiment is identical with the second embodiment in theorder of transmission of the position signal DS_pos and the commandsignal US_cmd. However, the third embodiment may be modified such thatthese signals are transmitted in the same order as in the firstembodiment.

The foregoing is a description of the preferred embodiments of thepresent disclosure. However, they are not intended to limit the scope ofthe present disclosure. Needless to say, the present disclosure will bevariously embodied within the scope of the disclosure.

For example, the second and third embodiments described above have thestylus 2 constructed such that the position signal DS_pos is transmittedfirst and then the data signal DS_res is transmitted, essentiallyrequiring use of the position signal DS_pos. The first embodiment,however, may function satisfactorily even in the case where the stylus 2does not transmit the position signal DS_pos. In this case, the tablet 3acquires the position information of the stylus from the data signalDS_res. This is illustrated in FIG. 12.

FIG. 12 is a diagram depicting the timing for signal reception andtransmission between the stylus 2 and the tablet 3 in a modification ofthe first embodiment. It depicts that the stylus 2 according to themodified embodiment transmits the signal “DS_others” instead of theposition signal DS_pos and the data signal DS_res. This modification ispossible in the first embodiment, in which the tablet 3 transmits thecommand signal US_cmd before receiving the position signal DS_pos.

A modification of the third embodiment employs the stylus 2 which hasthe internal structure and the internal configuration as depicted inFIGS. 17 and 18. Although the stylus 2 according to the third embodimentis provided with the electrode 21 which transmits the signals (DS_posand DS_res) and receives the signals (US_trg and US_cmd), the stylus 2according to the modified embodiment includes not only the electrode 21at the tip of the core 20 which transmits the signals (DS_pos andDS_res) but also the additional electrode 26 which receives the signals(US_trg and US_cmd). The additional electrode 26 is a ring-shapedelectrode attached close to the tip end of the body of the stylus 2, asdepicted in FIG. 17.

The stylus 2 according to the modified embodiment is configured asdepicted in FIG. 18, and operates in the same way as with the thirdembodiment (depicted in FIG. 10 and Table 3). In other words, thecontroller 70 performs control in such a way that when the SW4 selectsthe terminal a (as depicted in Table 3), the SW5 selects the terminal a(as depicted in FIG. 18), and the controller 70 performs control in sucha way that when the SW4 selects the terminal b (as depicted in Table 3),the SW5 selects the terminal b (as depicted in FIG. 18). Also, thestylus 2 according to the modified embodiment operates in the same wayas the third embodiment if it is configured in such a way that when theSW4 selects the terminal c (as depicted in Table 3), the SW5 selects theterminal b and the control signal En is left inactive (as depicted inFIG. 18). This configuration avoids activating the command informationreceiver 64 based on a determination that the electrode 26 is connectedto the command information receiver 64. It is also possible to configurethe embodiment such that the SW5 does not selects either the terminal aor the terminal b.

The stylus (depicted in FIG. 18) according to the modified embodiment isconfigured such that the electrode for signal transmission is connecteddirectly to the boosting circuit 74. This permits decreasing thecapacity of the output terminal of the boosting circuit 74, therebyreducing power consumption in the boosting circuit 74.

Each of the foregoing embodiments is designed such that the stylus 2 hasa battery for power supply. However, the battery may be replaced by asuper capacitor combined with a charging circuit.

Moreover, each of the foregoing embodiments is designed such that thepen pressure is converted into digital information, which issubsequently transmitted after OOK demodulation or BPSK demodulation.This configuration may be modified such that the frequency of positionsignal DS_pos is altered in accordance with the pen pressure, forexample.

DESCRIPTION OF REFERENCE SYMBOLS

-   1 Position detection device-   2 Stylus-   3 Tablet-   3 a Sensor surface of tablet 3-   4 Finger-   20 Core-   20 a Tip of core 20-   21, 26 Electrode-   23 Pen pressure detecting sensor-   24 Circuit board-   25 Battery-   30 Sensor-   30X, 30Y Linear electrode-   31 Sensor controller-   41 X-selecting circuit-   43 Y-selecting circuit-   43 Control circuit-   43 a Trigger signal transmitter-   43 b Command signal transmitter-   44, 45 Switch-   46, 63 a Amplifying circuit-   47 Gain control circuit-   48, 71 a Band-pass filter-   49, 63 b Demodulating circuit-   50, 64 a AD converter-   51 MCU-   60, 70 Controller-   61 Oscillating circuit-   61 a LC resonance circuit-   62 Transformer-   63, 71 Trigger signal detector-   64 Command information receiver-   64 b Matched filter circuit-   73 Transmitting signal generating circuit-   74 Boosting circuit-   SW1 to SW5 Switch

1. A position detection device configured to obtain a position pointedto by a position indicator on a tablet through capacitive couplingbetween the position indicator and the tablet, the position detectiondevice comprising: the tablet, which includes a first control signaltransmitter and a second control signal transmitter which, in operation,respectively transmit to the position indicator two types of controlsignals for controlling the position indicator, the two types of controlsignals differing from each other in terms of one or both of a frequencyand a modulation method; and the position indicator, which include apower source, a position indicating signal transmitter that in operationtransmits at least a position indicating signal to the tablet, a firstcontrol signal receiver that in operation receives a first controlsignal transmitted from the first control signal transmitter, and asecond control signal receiver that in operation receives a secondcontrol signal transmitted from the second control signal transmitter.2. The position detection device according to claim 1, wherein: thefirst control signal is a signal having a defined single frequency andnot modulated; and the second control signal is a signal modulated withdefined binary data.
 3. The position detection device according to claim2, wherein the first control signal receiver includes a filter circuitthat in operation passes certain frequencies around the defined singlefrequency.
 4. The position detection device according to claim 2,wherein the second control signal is a signal obtained by spreading thedefined binary data with a spread code.
 5. The position detection deviceaccording to claim 2, wherein the second control signal is a signalobtained by frequency-modulating a carrier wave with the defined binarydata.
 6. The position detection device according to claim 1, wherein:the position indicator is operable in a first operation mode to onlyreceive the first control signal and in a second operation mode totransmit at least the position indicating signal and receive the secondcontrol signal repeatedly, and in response to reception of the firstcontrol signal in the first operation mode, a transition occurs from thefirst operation mode to the second operation mode.
 7. The positiondetection device according to claim 1, wherein the tablet in operationtransmits the second control signal subsequent to a transmission of thefirst control signal.
 8. The position detection device according toclaim 1, wherein: the position indicator in operation receives the firstcontrol signal and thereafter transmits the position indicating signal;and the tablet in operation receives the position indicating signal andthereafter transmits the second control signal.
 9. The positiondetection device according to claim 1, wherein the position indicatorincludes at least one of unique ID information and a pen pressuredetection circuit and, in operation, transmits a data signal modulatedaccording to the unique ID information or pen pressure informationdetected by the pen pressure detection circuit.
 10. The positiondetection device according to claim 9, wherein the position indicator inoperation selects the unique ID information, or the pen pressureinformation, or other information in response to the received secondcontrol signal and transmits the data signal modulated according to theselected information.
 11. The position detection device according toclaim 9, wherein the data signal to be transmitted by the positionindicator is an On/Off Key (OOK)-modulated signal.
 12. The positiondetection device according to claim 9, wherein the data signal to betransmitted by the position indicator is a Binary Phase Shift Keying(BPSK)-modulated signal.
 13. A position indicator for deriving aposition pointed to by the position indicator on a tablet throughcapacitive coupling between the position indictor and the tablet, theposition indicator comprising: a power source; a position indicatingsignal transmitter that in operation transmits at least a positionindicating signal to the tablet; a first control signal receiver that inoperation receives a first control signal of a defined frequencytransmitted from the tablet; and a second control signal receiver thatin operation receives a second control signal modulated with definedbinary data and transmitted from the tablet.
 14. The position indicatoraccording to claim 13, wherein the first control signal receiverincludes a filter circuit that in operation passes certain frequenciesaround the defined frequency.
 15. The position indicator according toclaim 13, wherein the second control signal receiver in operationreceives a signal generated by spreading the defined binary data with aspread code.
 16. The position indicator according to claim 13, whereinthe second control signal receiver in operation receives a signalgenerated by frequency-modulating a carrier wave with the defined binarydata.
 17. The position indicator according to claim 13, which isoperable in a first operation mode to only receive the first controlsignal and in a second operation mode to transmit at least the positionindicating signal and receive the second control signal repeatedly;wherein in response to reception of the first control signal in thefirst operation mode, a transition occurs from the first operation modeto the second operation mode.
 18. The position indicator according toclaim 13, which includes at least one of unique ID information and a penpressure detection circuit and which, in operation, transmits a datasignal modulated according to the unique ID information or pen pressureinformation detected by the pen pressure detection circuit.
 19. Theposition indicator according to claim 18, which in operation selects theunique ID information, or the pen pressure information, or otherinformation in response to the received second control signal andtransmits the data signal modulated according to the selectedinformation.
 20. The position indicator according to claim 18, whereinthe data signal is an On/Off Key (OOK)-modulated signal.
 21. Theposition indicator according to claim 18, wherein the data signal is aBinary Phase Shift Keying (BPSK)-modulated signal.
 22. A positionindicator for deriving a position pointed to by the position indicatoron a tablet through capacitive coupling between the position indictorand the tablet, the position indicator comprising: a power source; atransformer having a primary coil and a secondary coil; a transmittingsignal generating circuit that in operation generates a signal having aresonance frequency of a resonance circuit formed of the primary coil ofthe transformer and a capacitor; an electrode connected to the secondarycoil of the transformer; and a control signal receiving circuit that inoperation receives a control signal transmitted from the tablet that hasa frequency close to the resonance frequency of the resonance circuit.